Methane (CH4) is an abundant natural resource as the main constituent of natural gas and oil-associated gases. However, methane has a configuration that renders it thermodynamically stable thereby inhibiting efficient utilization, e.g., as a fuel. Conversion of methane to other valued-added materials, such as C2 hydrocarbons (e.g., acetylene, ethylene, ethane) and higher hydrocarbons such as aromatics (e.g., benzene and naphthalene), which combined are referred to as C2+ hydrocarbons, is thus necessary.
Conversion of methane to other components can occur via indirect conversion or direct conversion (i.e., oxidative coupling of CH4 to C2+ hydrocarbons or non-oxidative direct methane conversion (NDMC)). In indirect conversion, methane is first converted to an intermediary (e.g., syngas (CO+H2)) using partial oxidation or by reforming. The value-added materials can then be formed by converting from the intermediary, for example, using Fischer-Tropsch synthesis of higher hydrocarbons. In oxidative coupling of CH4, the more reactive nature of C2+ products as compared to methane leads to undesired sequential oxidation of C2+ to thermodynamically favored COx (i.e., either CO or CO2). Such indirect or oxidative coupling conversions are, however, susceptible to high production and environmental costs, in particular large carbon dioxide emissions.
In contrast, NDMC forms C2+ hydrocarbons and H2 while avoiding the intermediate energy intensive steps required by the indirect or oxidative coupling conversion approaches. However, existing NDMC efforts suffer from kinetic and thermodynamic constraints that yield low CH4 conversion at practical reaction conditions.